The present invention relates to a device for and method of testing semiconductor laser module.
Recently, a higher-speed and larger-capacity communication art has been desired in accordance with widespread use of the Internet and the like, and therefore attention is paid to an optical communication art. FIG. 1 shows a configuration of a conventional testing device of a semiconductor laser module used as a key device in the optical communication art.
The testing device 1 is constituted by a measuring jig 11 which mounts a semiconductor laser module 2, an I-L measuring unit 12 which drives the semiconductor laser module 2 and obtains and computes an electricity-light characteristic, and a computer 13 which designates the setting to a constituted measuring system, operations, and data transfer and controls a series of measurement flows. The testing device is also constituted by an optical power detecting photodiode 14 which detects optical power of light output from the semiconductor laser module 2, a wavelength measuring instrument 15 which counts the number of wavelengths of the light output from the semiconductor laser module 2, and a temperature controller 16 which controls the temperature in the semiconductor laser module 2. A Peltier device is generally set in the semiconductor laser module 2 as a temperature control device and a thermistor (temperature sensor) is set therein as a temperature monitor. The temperature controller 16 controls the current to be supplied to the Peltier device and detects the temperature of a semiconductor laser by the thermistor.
In general, a test about a semiconductor laser is performed by setting a temperature to a constant temperature (e.g. 25xc2x0 C.) or a wavelength to a specific wavelength. The following is a procedure for a test of setting (tuning) a wavelength to a specific wavelength and measuring an optical output at the wavelength. First, the semiconductor laser module 2 is set to the measuring jig 11. Moreover, an optical fiber 21 extending from the module 2 is connected to an optical fiber 17 connected to the optical power detecting photodiode 14 and wavelength measuring instrument 15 via a connector (not shown). Then, a measuring program is started by the computer 13 to start a series of measurements.
When measurement is started, the inside of the semiconductor laser module 2 is set to a predetermined temperature such as 25xc2x0 C. by the temperature controller 16. This temperature is temporarily set to start measurement. Then, a predetermined current is supplied from the I-L measuring unit 12 to the semiconductor laser module 2 and a semiconductor laser is driven. At this point of time, a wavelength is confirmed on the basis of the light output from the semiconductor laser module 2 introduced to a wavelength measuring instrument 15.
A wavelength measured by the wavelength measuring instrument 15 is compared with a wavelength as a target (hereafter referred to as target wavelength). The temperature in the semiconductor laser module 2 is controlled by the temperature controller 16 on the basis of the comparison result, and the setting (tuning) to the target wavelength is performed. These operations are repeated until a measured wavelength coincides with the target wavelength. When a measured wavelength reaches the target wavelength, temperature information is read. At the same time, the optical output of the semiconductor laser module 2 is also read. These read values are stored in the computer 13 as measured data. The above explanation includes explanation about a flow of a program with regard to operation after a measuring program is started.
Recently, attention is paid to a wavelength locker module which is able to extremely accurately fix the wavelength of output light as compared with the case of a conventional semiconductor laser module. The wavelength locker module is provided with a wavelength monitor which outputs the wavelength of the light output from a semiconductor laser by converting the wavelength into an intensity. The wavelength monitor is constituted by a wavelength-light intensity converter such as a Fabry-Perot etalon and a light receiving device such as a photodiode. The Fabry-Perot etalon has a characteristic of transmitting the light having a specific wavelength and a characteristic that quantities of transmitted light are changed when wavelengths of the transmitted light are changed.
Therefore, by guiding the light output from a semiconductor laser to a Fabry-Perot etalon and photoelectrically converting the transmitted light by a photodiode, the wavelength of the light output from the semiconductor laser is converted into the intensity of a photoelectric current. The wavelength of the output light is kept constant by feeding back the intensity of the photoelectric current to temperature control of the semiconductor laser and controlling the temperature of the semiconductor laser so that the wavelength of the output light becomes constant at a target wavelength.
To fix an output wavelength of the wavelength locker module to a target wavelength, it is important to use the temperature information of a semiconductor laser when the output wavelength is fixed to the target wavelength and the output values (this is referred to as locking point) of a wavelength monitor. Therefore, it is necessary to apply a test for finding the locking point to the wavelength locker module. Moreover, it is necessary to perform various static characteristic tests and dynamic characteristic tests including a transmission test as an optical semiconductor in a state fixed at a locking point, that is, a state in which the semiconductor laser is operated by feeding back an output of the wavelength monitor to temperature control of the semiconductor laser.
However, conventionally, there is no means to control the temperature of a semiconductor laser on the basis of an output of a wavelength monitor when testing a wavelength locker module. Therefore, there is a problem that it is difficult to quickly and properly perform a test for finding a locking point and various characteristic tests in a state fixed at the locking point.
It is an object of this invention to provide a device for and method of testing a semiconductor laser module for applying tests of various characteristics as an optical semiconductor to modules as follows while fixing a wavelength. More specifically, one of the modules is a wavelength locker module having a function for locking a wavelength by feeding back the wavelength of the output light detected by a wavelength monitor and controlling a temperature of the module, and another module is a wavelength variable laser module using the wavelength locking function.
In the semiconductor laser module testing device according to one aspect of this invention, the semiconductor laser module is provided with a semiconductor laser, a wavelength monitor for detecting a wavelength of light output from the semiconductor laser, and a temperature control device for controlling a temperature of the semiconductor laser. The semiconductor laser module testing device comprises a wavelength feedback circuit which compares a wavelength detected by the wavelength monitor of the semiconductor laser module with a target wavelength, and outputs a comparison signal corresponding to a result of the comparison. The testing device also comprises a processor which outputs a control signal corresponding to the comparison signal supplied from the wavelength feedback circuit, and a temperature control power source which controls power to be supplied to the temperature control device based on the control signal supplied from the processor.
In the semiconductor laser module testing device according to another aspect of this invention, the semiconductor laser module is provided with a semiconductor laser, a wavelength monitor for detecting a wavelength of light output from the semiconductor laser, a temperature control device for controlling a temperature of the semiconductor laser, and a temperature monitor for detecting a temperature of the semiconductor laser. The semiconductor laser module testing device comprises a wavelength feedback circuit which compares a wavelength detected by the wavelength monitor of the semiconductor laser module with a target wavelength, and outputs a comparison signal corresponding to a result of the comparison. The testing device also comprises a temperature feedback circuit which compares the temperature detected by the temperature monitor with a set temperature, and outputs a comparison signal corresponding to a result of the comparison. The testing device further comprises a processor which outputs a control signal corresponding to the comparison signal supplied from the wavelength feedback circuit or the temperature feedback circuit, and a temperature control power source which controls power to be supplied to the temperature control device based on the control signal supplied from the processor.
In the method of testing a semiconductor laser module according to still another aspect of this invention, the semiconductor laser module provided with a semiconductor laser, a wavelength monitor for detecting a wavelength of light output from the semiconductor laser, and a temperature control device for controlling a temperature of the semiconductor laser. The method of testing the semiconductor laser module comprises a step of obtaining a correlation between a temperature of the semiconductor laser and a wavelength of the light output therefrom based on a change amount of the temperature when the temperature of the semiconductor laser is changed by controlling power to be supplied to the temperature control device, and on a change amount of the wavelength detected by the wavelength monitor.
In the method of testing a semiconductor laser module according to still another aspect of this invention, the semiconductor laser module provided with a semiconductor laser, a wavelength monitor for detecting a wavelength of light output from the semiconductor laser, a temperature control device for controlling a temperature of the semiconductor laser, and a temperature monitor for detecting a temperature of the semiconductor laser. The method of testing the semiconductor laser module comprises a step of obtaining a correlation between a temperature of the semiconductor laser and a wavelength of the light output therefrom based on a change amount of the temperature when the temperature of the semiconductor laser is changed by controlling power to be supplied to the temperature control device while detecting the temperature of the semiconductor laser by the temperature monitor, and on a change amount of the wavelength detected by the wavelength monitor.
Other objects and features of this invention will become apparent from the following description with reference to the accompanying drawings.